1. Field of the Invention
The present invention relates to current-perpendicular-to-the-plane (CPP) magnetic sensing elements and, more particularly, to a magnetic sensing element in which read sensitivity and read output can be improved even when the track is narrowed.
2. Description of the Related Art
FIG. 7 is a partial sectional view of a conventional CIP magnetic sensing element, viewed from the surface facing a recording medium. Herein, CIP stands for current-in-the-plane, and in the CIP magnetic sensing element, a sensing current flows parallel to the planes of a multilayer film which is located in the center of the magnetic sensing element.
Referring to FIG. 7, the magnetic sensing element includes a lower shielding layer 1 composed of Permalloy (NiFe alloy) or the like and a lower gap layer 2 composed of Al2O3 or the like disposed thereon.
On the lower gap layer 2, an underlayer 3, a seed layer 4, a first antiferromagnetic layer 5, a pinned magnetic layer 6, a first nonmagnetic layer 7, a free magnetic layer 8, a second nonmagnetic layer 9, and a second antiferromagnetic layer 10 are deposited, and the laminate from the underlayer 3 to the second antiferromagnetic layer 10 is hereinafter referred to as a multilayer film 11.
The first antiferromagnetic layer 5 is composed of an antiferromagnetic material, such as a PtMn alloy, each of the pinned magnetic layer 6 and the free magnetic layer 8 is composed of a ferromagnetic material, such as a NiFe alloy, and the first nonmagnetic layer 7 is composed of a nonmagnetic conductive material, such as Cu.
End faces 11a at both sides in the track width direction (in the X direction) of the multilayer film 11 are formed by etching. Although the end faces 11a extend perpendicular to a plane (X-Y plane) parallel to the planes of the multilayer film 11 in the drawing, the end faces 11a are actually inclined planes.
A track width Tw is determined by the width in the track width direction (in the X direction) of the free magnetic layer 8. As the recording density is increased, the track width Tw is considerably decreased.
Electrode layers 12 are formed on the end faces 11a of the multilayer film 11. As shown in FIG. 7, an upper gap layer 13 composed of Al2O3 or the like extends over the multilayer film 11 and the electrode layers 12, and an upper shielding layer 14 composed of Permalloy or the like is disposed on the upper gap layer 13.
In the conventional magnetic sensing element shown in FIG. 7, the second antiferromagnetic layer 10 is formed on the free magnetic layer 8 with the second nonmagnetic layer 9 therebetween. In such a structure, unidirectional interlayer exchange coupling occurs between the second antiferromagnetic layer 10 and the free magnetic layer 8, and a unidirectional longitudinal bias magnetic field is applied to the free magnetic layer 8.
If the interlayer exchange coupling magnetic field is too strong, the sensitivity of the free magnetic layer 8 to an external magnetic field is weakened. The magnitude of the interlayer exchange coupling can be controlled by changing the thickness of the second nonmagnetic layer 9.
As track narrowing is accelerated, the means for applying the longitudinal bias magnetic field shown in FIG. 7 is considered as one of the optimum means.
As described above, the magnetic sensing element shown in FIG. 7 is a CIP magnetic sensing element in which a sensing current flows parallel to the planes of the multilayer film 11. Recently, attention is being given to a current-perpendicular-to-the-plane (CPP) magnetic sensing element in which read output can be increased even if the element is miniaturized.
FIG. 8 is a longitudinal sectional view of a CPP magnetic sensing element using the means for applying the longitudinal bias magnetic field described with reference to FIG. 7, viewed from the surface facing a recording medium.
A multilayer film 11 shown in FIG. 8 has the same structure as that shown in FIG. 7 except that electrode layers 16 and 15 are provided on the upper and lower faces in the thickness direction (in the Z direction) of the multilayer film 11, respectively, and insulating layers 17 composed of Al2O3 or the like are formed at both sides in the track width direction (in the X direction) of the multilayer film 11.
In the CPP magnetic sensing element, a sensing current flows parallel to the thickness direction of the multilayer film 11. Consequently, the electrode layers 16 and 15 are provided on the upper and lower faces in the thickness direction of the multilayer film 11, respectively.
In the CPP magnetic sensing element, in order to effectively improve the read output, the product (ΔR×A) of a change in resistance ΔR and an area A of the plane (X-Y plane) parallel to the planes of the multilayer film 11 must be increased.
An increase in the thickness h1 of the free magnetic layer 8 has been considered to be one method for gaining the product (ΔR×A) under the situation of miniaturization of the element with track narrowing.
However, if the thickness h1 of the free magnetic layer 8 is increased, the demagnetizing field of the free magnetic layer 8 is increased, resulting in a degradation in the read sensitivity η.
An attempt has been made to control the magnetization of the free magnetic layer 8 by strengthening the interlayer exchange coupling generated between the free magnetic layer 8 and the second antiferromagnetic layer 10 so as to counteract the demagnetizing field.
The strength of the interlayer exchange coupling can be controlled by changing the thickness of the second nonmagnetic layer 9 interposed between the free magnetic layer 8 and the second antiferromagnetic layer 10. However, if the interlayer exchange coupling is strengthened, although the influence of the demagnetizing field may be weakened, since a strong unidirectional longitudinal bias magnetic field is applied to the free magnetic layer 8, the magnetic reversal of the free magnetic layer 8 becomes insensitive to an external magnetic field or does not occur. As a result, it is not possible to fabricate a magnetic sensing element with excellent read sensitivity.
That is, in any case, in the conventional CPP magnetic sensing element having a structure including the means for applying the longitudinal bias magnetic field shown in FIG. 7, it is not possible to improve read sensitivity η and read output simultaneously.